Few-layer Black Phosphorous Catalyzes Radical Additions to Alkenes Faster than Low-valence Metals

Article abstract of DOI:10.1002/cctc.201902276

The substitution of catalytic metals by p-block main elements has a tremendous impact not only in the fundamentals but also in the economic and ecological fingerprint of organic reactions. Here we show that few-layer black phosphorous (FL-BP), a recently

Full text of DOI:10.1002/cctc.201902276

Accepted Article
Title: Few–layer black phosphorous catalyses radical additions to
alkenes faster than low–valence metals
Authors: Maria Tejeda-Serrano, Vicent Lloret, Bence G. Márkus,
Ferenc Simon, Frank Hauke, Andreas Hirsch, Antonio
Doménech–Carbó, Gonzalo Abellán, and Antonio Leyva–
Pérez
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10.1002/cctc.201902276
ChemCatChem
FULL PAPER
Few–layer black phosphorous catalyses radical additions to
alkenes faster than low–valence metals
María Tejeda–Serrano,a Vicent Lloret,b Bence G. Márkus,c Ferenc Simon,c Frank Hauke,b Andreas
Hirsch,b Antonio Doménech–Carbó,d,* Gonzalo Abellánb,e,* and Antonio Leyva–Péreza,*
Abstract: The substitution of catalytic metals by p–block main
elements has a tremendous impact not only in the fundamentals but
also in the economic and ecological fingerprint of organic reactions.
Here we show that few–layer black phosphorous (FL–BP), a recently
discovered and now readily available 2D material, catalyses different
radical additions to alkenes with an initial turnover frequency (TOF0)
up to two orders of magnitude higher than representative state–of–
the–art metal complex catalysts at room temperature. The
corresponding electron–rich BP intercalation compound (BPIC) KP6
shows a nearly twice TOF0 increase with respect to FL–BP. This
increase in catalytic activity respect to the neutral counterpart also
occurs in other 2D materials (graphene vs. KC8) and metal complex
catalysts (Fe0 vs. Fe2- carbon monoxide complexes). This reactive
parallelism opens the door for cross–fertilization between 2D
materials and metal catalysts in organic synthesis.
involve a two–electron rather than a one–electron redox process,
since the latter is generally more difficult to handle for p–block
main elements beyond photoinduced processes.[6b] Looking back
into the analogies between late–heavy and first–row transition
metals, one finds that the ordered aggregation of metals in the
form of clusters and nanoparticles enables encumbered
electronic states, otherwise severely restricted in atomic systems,
since the metal atoms cooperate to stabilize intermediate, atypical
electronic states.[7] This effect is particularly effective for low–
valence states and, for instance, reduced gold nanoparticles act
as electron sinks for catalytic radical reactions that otherwise
would not occur.[8] Following this rationale, one might expect that
redox–active p–block elements in low oxidation state will enable
radical reactions after stabilization of electron–rich intermediates
by a suitable designed atomic network. In this sense,[9] post–
graphene monoelemental two dimensional (2D) materials of
Group 15, also called 2D–pnictogens (P, As, Sb, and Bi),
represent a promising alternative due to their large chemically
active surface and their ability to adsorb and stabilize unsaturated
organic molecules through van der Waals interactions.[10]
Specifically, black phosphorus (BP) consists of sp3 hybridized P
atoms showing a puckered structure with a dative electron lone
pair located on every surface atom (Figure 1a). The availability of
these surface atom orbitals for external reactants together with
the cooperativity of the atomic network and the possibility of
breaking temporarily P–P bonds to exchange one electron,[11]
would make, in principle, this 2D material a potential catalyst for
radical reactions. To the best of our knowledge, examples of neat
P aggregates as catalysts in organic synthesis are very scarce,[12]
besides P alloyed metal nanoparticles.[13]
Introduction
The search for p–block main element compounds to
substitute generally more toxic, expensive and less available
metal catalysts, is a current topic of much interest.[1] The
replacement of late–heavy by first–row transition metals, based
on isovalence, isoelectronics and isolobal orbital analogies,
among others,[2] has been continued with metal–free soluble
nitrogen–, sulfur– and phosphorous–containing molecules,[3]
including insoluble compounds such as graphene,[4] fullerenes[5]
and carbon nitrides.[6] However, most of the examples reported
[a]
[b]
[c]
M. Tejeda–Serrano, Dr. A. Leyva–Pérez, Instituto de Tecnología
Química. Universidad Politècnica de València–Consejo Superior de
Investigaciones Científicas. Avda. de los Naranjos s/n, 46022,
Valencia, Spain. E–mail: anleyva@itq.upv.es.
V. Lloret, Dr. F. Hauke, Prof. A. Hirsch, Dr. G. Abellán, Friedrich–
Alexander–Universität Erlangen–Nürnberg (FAU) Nikolaus–Fiebiger
Straße 10, 91058 Erlangen and Dr.–Mack Straße 81, 90762 Fürth,
Germany. E–mail: gonzalo.abellan@fau.de.
Department of Physics, Budapest University of Technology and
Economics, POBox 91, H–1521 Budapest, Hungary and MTA–BME
Lendület Spintronics Research Group (PROSPIN), POBox 91, H–
1521 Budapest, Hungary.
Prof. A. Doménech–Carbó, Departamento de Química Analítica.
Universitat de València. Dr. Moliner, 50, 46100, Burjassot, València,
Spain. E–mail: Antonio.Domenech@uv.es.
Results and Discussion
-
Synthesis of few–layer black phosphorus (FL–BP).
In order to study radical reactions catalysed by BP nanosheets in
conventional organic solvents, liquid phase exfoliation (LPE) of
bulk BP into high–quality few–layers (FL–BP) has been
developed in a two–step process. Firstly, dispersions of BP in
NMP were obtained in an Ar–filled glove–box (<0.1 ppm O2 and
<0.1 ppm H2O), avoiding oxidation and decomposition of the
catalyst.[14] Afterwards, the FL–BP was transferred to THF by
sequential ultracentrifugation and re–dispersion, leading to stable
dispersions with a P concentration of 0.001 wt% determined by
ICP and with <0.01 wt% of NMP (See experimental in SI for a
detailed procedure). Figure 1c shows an excellent wide–area
correlation between topographic atomic force microscopy (AFM)
[d]
[e]
Dr. G. Abellán, Instituto de Ciencia Molecular (ICMol), Universidad
de ValenciaCatedrμtico José Beltrán 2, 46980, Paterna, Valencia
Spain.
Supporting information for this article, including the experimental
and characterization part; additional comments, Tables and Figures;
and NMR copies, is given via a link at the end of the document.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201902276
ChemCatChem
FULL PAPER
and scanning Raman microscopy (SRM) of the as–prepared
nanosheet dispersions spin–coated on SiO2/Si wafers. The
sample statistics show FL–BP flakes 11.5 nm in thickness and
45–475 nm in lateral dimensions (Figure 1b and SI1). The A1 /A2
> 0.4 intensity ratio statistics (average 0.79) indicate the absence
of oxidation (see Figures S1 and S2 for additional
characterization).[12b,15]
(entry 6). The reaction with FL–BP catalyst can be run at ten–time
higher scale without significant depletion in the catalytic activity
(see SI), to give a 50% isolated yield of 3. Other representative
2D and redox–active nanoparticulated materials such as
graphene, single–walled carbon nanotubes (SWCNT), boron
nitride, nanotitania, nanoceria and, remarkably, pristine, non–
exfoliated BP, do not catalyse the reaction (entries 3–8) at any
catalyst loading tested. In contrast, the more electron–rich black
phosphorus intercalation compound (BPIC) material KP6,[18]
which basically consists of K atoms intercalated between the FL–
BP structure (similarly to alkali graphite intercalated compounds,
GICs) and donating its odd electron to the 2D structure, gives the
g
g
highest TOF0 of all compounds tested, although with a lower final
yield of 3 (10 s-1, entry 9), and the GIC KC8
also showed an
[19]
excellent TOF0= 0.76 s-1 and 52% yield (entry 10). These results
suggest that the more electron rich the 2D material, the higher the
catalytic activity.
To gain further insights into the by FL–BP catalyzed radical
coupling reaction, we followed the reaction between 1–hexene 4
and CBrCl3 2 in–situ by liquid Raman spectroscopy, cyclic
voltammetry, gas–chromatography coupled to mass spectrometry
(GC–MS) and nuclear magnetic resonance (NMR), which allows
the simultaneous identification and characterization of reagents,
products and the FL–BP catalyst during reaction.
Table 1. Catalytic results for the radical coupling between 1 and 2.
The new formed bonds are highlighted in black. The catalyst mol% is
the lowest to achieve maximum TOF0 after 24 h.
Catalyst (0.005-5 mol%)
+
CBrCl3
CCl3
6
6
THF (0.25 M), 25 ºC, N2
Br
3
1
2
TOF0 (s-1)
Yield (3, %)
Entry
Catalyst (mol%)
Figure 1. a) Schematic representation of the BP structure highlighting
the presence of lone pair electrons. b) General scheme of the liquid
phase exfoliation and sequential solvent exchange process from NMP
to THF. c) Wide area Scanning Raman Microscopy image of FL–BP
deposited on Si–SiO2 substrates. d) corresponding AFM image. e)
Histogram of the apparent thickness of the exfoliated FL–BP obtained
from AFM. The inset shows an AFM image of two nanosheets along
with its corresponding height profile of ca. 11 and 12 nm, respectively.
f) Plot of the nanosheet length as a function of the flake height
considering a total amount of 170 replicates. The average thickness
is H= 11.5±0.2 nm and lateral sizes are ranging from 45 to 475 nm.
1
2
FL–BP (0.005)
Fe(CO)5 (5)
Graphene (5)
SWCT (5)
7.123
51
60
0
0.014
3
–
4
–
0
5
Boron nitride (5)
Nanotitania (5)
Nanoceria (5)
BP (0.005–5)
KP6 (3)
–
0
6
–
0
7
–
0
8
–
0
9
10.036
6
10
11
12
13
14
15
KC8 (5)
0.765
52
81
0
-
Radical addition of perhalomethanes to alkenes.
Na2Fe2(CO)8 (5)
FeCl3 (5)
0.018
–
–
–
–
Table 1 shows the catalytic results for a challenging metal–
CuCl (5)
0
catalysed radical reaction at room temperature, i.e. the coupling
between 1–decene 1 and CBrCl3 2, which generally requires to
proceed >0.1 mol% of metal catalyst without radical promoters, a
high excess of 2 (generally employed as a solvent) and/or heating
conditions (see Tables S1 and S2 for a complete set of catalysts
and reaction conditions).[16] In contrast to any previous metal
catalyst, FL–BP catalyses the coupling with 0.005 mol% and a
TOF0≈7.1 s-1 (entry 1), almost 3 orders of magnitude higher than
the well–known catalyst Fe(CO)5,[17] where the TOF0 is 0.014 s-1
NiCl2 (5)
0
RuCl2(PPh3)2 (5)
0
Figure 2 shows the Raman spectra of the FL–BP dispersion in
THF (t= 0 h), in which the A1 , B2g and A2 BP vibrational bands
can be seen at 362, 440 and 466 cm-1, respectively (see also
g
g
Figures S3–5). In turn, the Raman spectra of 4, presents a main
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10.1002/cctc.201902276
ChemCatChem
FULL PAPER
characteristic band at 1641 cm-1 (Figure S5), which corresponds
to the strong and polarized alkene C=C stretching vibration,
whereas CBrCl3 presents six bands in total: a main vibrational
mode at 423 cm-1, three bending modes at 191, 247 and 294 cm-
1, and two stretching bands at 719 and 776 cm-1 (see control
spectra of the pure compounds and THF in Figures S3 and S5).[20]
In presence of FL–BP, the coupling between 4 and 2 leads to the
product 3–bromo–1,1,1–trichloroheptane 5 (t= 10 h), in which the
C–Br vibration decreases to give a characteristic band at 372 cm-
1, and three Raman bands emerge at 168, 224 and 275 cm-1.
Figure 2 also shows the cyclic voltammograms recorded during
the reaction between 1 and 2 with (black) and without (red) FL–
BP as a catalyst (1 remains silent under the experimental
conditions and the voltammogram of 2 can be seen in Figure S6).
The intensity of both the reduction and the coupled oxidation
signals of 2 (CRX and Ax, respectively) decreases in the presence
of the FL–BP catalyst, and this intensity further decreases with
additional FL–BP amounts (Figure S7). However, no apparent
changes in the oxidation state of P occur, in contrast with the clear
oxidation that suffers FL–BP when the reactants are not present
(Figure S8).[21] The stability FL–BP after the reaction was also
evaluated by SRM by drop casting the dispersions in SiO2 wafers
and washing with 2–propanol and acetone (Figure S9), and the
PBN EPR signal (see also Figure S24 d) due to the formation of PBN–
CCl3 adduct in presence of FL–BP in THF.
that the structure remains un–oxidized after the reaction. These
electrochemical and spectroscopic data support that FL–BP
catalyses the radical coupling between 1 (or 4) and 2, and that the
P atoms do not change its oxidation state during reaction.
The fact that pristine BP is inactive as a catalyst (entry 8 in
Table 1) suggests that a previously well–delaminated BP material
is essential for the catalysis. Indeed, four new samples of FL–BP
with different concentrations were prepared by dilution of a same
mother dispersion (Figure S10) and the radical reaction was only
catalysed by the well exfoliated, low concentrated FL–BP
dispersions and not by any BP sample at >1 mM concentration
(see Figure S2). In–situ Raman and SRM studies (Figures S11
and 12) show the rapid disappearance of the characteristic KP6
intercalation bands at around 290 and 400 cm-1, which confirms a
strong agglomeration of the KP6 flakes during reaction and
explains the rapid deactivation of this extremely active but
unstable catalyst (entry 9 in Table 1). These results confirm the
need of an exfoliated BP material to catalyse the radical coupling.
At this point, since the more electron–rich KP6 and KC8
catalyse the radical coupling between 1 and 2 faster than FL–BP
and graphene, respectively, different low–valence Fe1- and Fe2-
complexes[22] were prepared and tested as catalysts, and
compared with the benchmark catalyst Fe(CO)5. Table 1 (entry
11) shows the higher catalytic activity of Collman´s reagent
derivative Na2Fe2(CO)8 compared to Fe(CO)5 (see Table S1 for
other low–valence Fe complexes) and, by far, compared to other
metal catalysts (entries 11–15, notice that these metal salts only
catalyse the radical coupling with an excess of 2 under heating
conditions). Low–valence Fe complexes are routinely used as
reagents for 2e- carbon–carbon couplings[23] but not so used as
catalysts for radical couplings.[24] Kinetic studies (Figures S13 and
S14) corroborate the high intrinsic catalytic activity of low–valence
Fe and indicate that Fe(CO)5 and Fe2+ salts may evolve under
reaction conditions to the more active low–valence Fe species,
according to in–situ Fourier–transform infrared spectroscopy (FT–
IR, Figure S15), 1H and 13C NMR (Figure S16) and
electrochemical measurements (Figures S17 and S18). Figure 3
shows that an array of bromo– and chloro–substituted trichloro,
and more challenging trifluoro–, alkyl compounds[25] 6–18 could
be synthesized under these mild reaction conditions, i.e.
equimolar amounts of alkene and alkyl halide at room
temperature for the atom–transfer radical addition (ATRA).
Moreover, Figure 4 shows that, under similar reaction conditions,
polymers 19–23 could be prepared after atom–transfer radical
addition polymerisation (ATRP) reactions. The products are
decorated with other functional groups such as hindered internal
alkenes, ketones, acid–sensitive silylethers and ethers, esters
and other halides, which cannot be done with previously reported
methodologies, particularly for natural products (Tables S2 and
S3, see Refs. therein). Thus, it can be said that the observed
increasing catalytic activity of 2D materials with electron richness
also applies to Fe complex catalysts and enables a new synthetic
procedure for sensitive organic compounds.
A1 /A2g ratio exhibits a value higher than 0.4, thus corroborating
g
Figure 2. a) In–situ liquid Raman spectra of BP in THF, after the
addition of 1–hexene 4 and CBrCl3 2 (t= 0 h), and after 10 h reaction
time. The BP modes can be observed during the reaction and the
corresponding bands of 2 disappear with time, giving rise to the new
spectroscopic bands of the product. The different vibrational modes
of C–Cl, Cl–C–Cl and C–Br are assigned with different colors. These
results have been backed by GC–MS and NMR analysis. b) Cyclic
voltammograms at glassy carbon electrode of a 10 mM 1 plus 10 mM
2 solution in 0.10 M Bu4NPF6/DMSO before (red) and after (black)
adding catalytic FL–BP. Potential scan rate 50 mV s-1. c) Emergent
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10.1002/cctc.201902276
ChemCatChem
FULL PAPER
(1-10 mol%)
X
catalysts, i.e. v0= kexp[catalyst][1][2]. The nature and bonding of
Na
2Fe(CO)4
R2
3-X
R2
+
R
R1
R1
the halide atom transferred from
2
was studied by
THF (0.5 M) or neat, N2
r.t.-120 ºC, 16 h
R3
(1 equivalent)
electrochemistry and the results show that only Br and not Cl
anions are released during the coupling with both FL–BP and
Na2Fe(CO)4 catalysts,[26] by a 1e- process (Figure S21).[27],[28]
Indeed, the results support the formation of a transient P–Br bond
after radical dissociation of 2[16a] and then coupling with alkene
1.[29] This mechanistic proposition nicely engages with the ability
of FL–BP to couple with alkyl halides by temporal breaking of
lattice P–P bonds[11] and also with the easy chemically–induced
polymerization of alkenes.[30] For low–valence Fe complexes, this
proposal is also validated by the crystallographic characterisation
of insertion products of perfluoromethane halides[31] and alkyl
chlorides[32] in Na2Fe2CO8. In the case of FL–BP, electron
paramagnetic resonance (EPR) proves the radical mechanism,
confirmed by the addition of the N–tert–butyl–α–phenylnitrone
(PBN) spin trap, which is known to work with CCl3 radicals.[33] In
the presence of FL–BP in THF, a homolytic cleavage of the C–Br
bond of CBrCl3 forms CCl3 radicals, which are rapidly trapped.
The intensity gain of the PBN bands is a clear signal of the
successful reduction of the molecule, and the characteristic N
triplet signal in Figure 2c appears due to a hyperfine coupling of
the electron to the nitrogen nuclei. The additional splitting of the
triplet is caused by H nuclei in the spin adduct PBN–CCl3, and no
other signals corresponding to the addition of Cl atoms to PBN
are observed (Figure S22). Altogether, these results strongly
support that the mechanism of both FL–BP and low–valence Fe
catalysts for the radical coupling of 1 and 2 is essentially the same,
also similar to typical metal catalysts, as shown in Figure 5.
Br
CCl3
CCl3
CCl3
(80%)
(83%)
Br
Br
Br
(75%)
6
3
7
Br
Br
CCl3
O
(55%)
(90%)
(65%)
9
8
10
Cl3C
Cl3C
I
(60%)
12
O
CCl3
Si
O
CCl3
Br
Br
(60%)
11
H
O
Br
O
H
H
O
H
(85%)
CCl3
13
Br
H
H
O
CF3
(78%)
CCl3
15
14
(56%)
Cl
Cl
CF3
O
Cl
CF3
CF3
O
6
6
(76%)
(50%)
(67%)
17
18
Cl
16
Figure 3. Radical additions of trihalomethyl halides to alkenes
catalysed by Na2Fe(CO)4. Specific reaction conditions: Products 3–14
isolated after 16 h at 25 ºC in THF (0.5 M) with 10 mol% catalyst;
products 15–18 isolated after 16 h at 120 ºC under solventless
conditions and with 1 mol% catalyst, CF3SO2Cl used as a reagent.
+
, Ru2+, Ni2+, Cu , Fe0,...
(this work)
X
X=Cl, Br; Cat= Fe2+
R
n
Catn
Fe1- Fe2-
R-X
R
,
, FL-BP, KP6, KC8
R´
Na
2Fe(CO)4
O
(1 mol%)
- Electron-rich without external aid
- Non acid-catalyzed competitive reactions
- Easy alkene coordination and halide transferring
R´
+
Br
XCatn+1
R
Polymer
OEt
Solventless, N
2
n
(0.01 equivalent)
ATRP
90 ºC, 1 h
R
ATRA
R´
O
Figure 5. Plausible mechanism for the FL–BP and low valence Fe–
catalysed atom–transfer radical addition (ATRA) and polymerisation
(ATRP) reactions. R= Ar, alkyl.
O
Br
OEt
100
Br
OEt
x
y
R=H (81%)
R=CH
R=CF 2(50%)
3
x:y= 75:25 (90%)
x:y= 90:10 (80%)
19
20
21
22
23
Cl (50%)
R
CH2Cl
-
Other radical additions to alkenes.
Figure 4. Radical polymerization catalysed by Na2Fe(CO)4. Products
19-23 isolated after 1 h at 90 ºC under solventless conditions and with
1 mol% catalyst. Polymerizations were not catalyzed by FL–BP under
the indicated reaction conditions.
Figure 6 shows the use of FL–BP as a catalyst for other
radical additions to alkenes typically catalyzed by Fe
compounds.[34] The results confirm the higher catalytic activity of
(FL–BP) for these radical couplings compared to the
representative Fe–based catalysts, under optimized conditions
for FL–BP and under reasonable mass scales. Notice that 25 and
28 were used as coupling partners since nitrobenzene derivatives
better adsorb and react on the FL–BP surface, thus taking
advantage of the adsorption properties of FL–BP to carry out the
catalysis.[12a]
-
Reaction mechanism.
In order to determine if the electronic parallelism found for
the main element 2D materials and metal complexes as catalysts
for the radical coupling of 1 and 2 does not only occur in reactive
but also in mechanistic terms, kinetic studies at different
concentrations of reagents either with FL–BP or Na2Fe(CO)4
catalyst were carried out (Figures S19 and S20, respectively). The
results give the same experimental rate equation for both
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10.1002/cctc.201902276
ChemCatChem
FULL PAPER
was purified by column chromatography eluting with heptane or
hexane/ethyl acetate to give the product as a clear oil (87 mg,
0.26 mmol, 51%), as analysed by GC, GC–MS, and NMR
spectroscopy.
Catalyst (5 mol%)
NaCl (2 eq.)
O
Catalyst Yield (%)
NH3
FL-BP
FeCl
55 (45)a
38
NH2
+
8
O
8
THF/MeOH/DCM
Cl
24
OTf
(2 eq.)
O2N
2
(1:1:0.2, 0.25 M),
16 h
26
-
17
25
25 ºC, N2,
Catalyst Yield (%)
S
NO2
Catalyst (5 mol%)
FL-BP
Fe(OTf)
-
82 (83)a
44
SH
Ph
Ph
Acknowledgements
+
Ph
THF (0.25 M), darkness,
25 ºC, N 16 h
Me
+
3
O2N
27
2,
<5
S
28
(2 eq.)
We thank the European Research Council (ERC Starting Grant
2D–PnictoChem 804110 to G.A. and ERC Advanced Grant
742145 B–PhosphoChem to A.H.). G.A. thanks the financial
support from the Spanish MINECO (Unit of Excellence “Maria de
Maeztu” MDM–2015–0538), the Generalitat Valenciana
29
Mixture of isomers,
NO2
Figure 6. Other radical additions to alkenes catalysed by FL–BP.
Reaction conditions optimised for FL–BP. GC yields. Tf:
trifluoromethanesulfonate. Between brackets, yields at ten–time
higher scale (0.5 and 1 mmol, respectively).
a
(CIDEGENT/2018/001
grant),
and
the
Deutsche
Forschungsgemeinschaft (DFG, FLAG–ERA AB694/2–1). M. T.–
S. thanks ITQ for a contract. A. L.–P. thanks financial support by
MINECO (Spain) (Projects CTQ 2014–55178–R, CTQ 2017–
86735–P and Excellence Unit “Severo Ochoa” SEV–2016–0683)
and also “Convocatoria 2014 de Ayudas Fundación BBVA a
Investigadores y Creadores Culturales”. B. G. M. and F. S. were
supported by the National Research, Development and
Innovation Office of Hungary (NKFIH) Grant Nrs. K119442 and
2017–1.2.1–NKP–2017–00001.
Conclusions
The 2D material FL–BP catalyzes with extraordinary activity
different radical additions to alkenes. The electron–rich
counterpart KP6 is even more catalytically active, and this
increase in catalytic activity with electron richness also applies not
only to other main element 2D materials such as graphene (vs.
KC8) but also to low–valence Fe complexes (vs. Fe0). The use of
catalytic FL–BP constitutes a seminal and very promising starting
point to design efficient radical catalysts based in 2D p–block
elements, and the parallelism found between 2D materials and Fe
complexes opens the door for cross–fertilization studies between
these two apparently separated catalytic areas.
Keywords: black phosphorus • p–block catalysis • radical
addition to alkenes • low–valence Fe • 2D material
[1]
[2]
R. L. Melen, Science 2019, 363, 479–484.
A. Corma, A. Leyva–Perez, M. J. Sabater, Chem. Rev.
2011, 111, 1657–1712.
[3]
a) B. Ines, D. Palomas, S. Holle, S. Steinberg, J. A. Nicasio,
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Experimental Section
Synthesis of FL–BP: LPE under inert conditions was achieved
by tip sonication in an argon–filled glovebox (<0.1 ppm O2 and
<0.1 ppm H2O). The starting concentration of BP was 2 mg mL-1
in NMP and the FL–BP was achieved by using a Bandelin
Sonoplus 3100, 80% amplitude, four intervals of 30 min (2h in
total), pulse 2 s on, 2 s off, stirring and cooling the dispersion (0°C)
to avoid high temperatures and the decomposition of BP flakes.
After the exfoliation, the FL–BP dispersion were centrifuged for
1h. at 1753 g, the supernatant was transferred to a new vial and
the dispersions were further centrifuged at 21475 g. The FL–BP
precipitate was separated from NMP and re–dispersed in
anhydrous THF. Solvent exchange was achieved after repeating
the last process 3 times, ensuring that most of the NMP has been
exchanged in the dispersion. The concentration of the dispersion
was quantified by ICP, presenting 0.001 wt% of phosphorus. The
concentration of the dispersions can be modified by appropriated
dilutions.
Typical reaction procedure for the reaction between 1–
decene 1 and CBrCl3 2 with FL–BP: In the glove box, 0.5 ml of
FL–BP (0.005 mol%) in dry THF was placed in a 2 mL vial
equipped with a magnetic stirrer. Then, 1–decene 1 (50 µl, 0.5
mmol, 1 eq) and CBrCl3 2 (25 µl, 0.5 mmol, 1 eq) were added.
The reaction mixture was magnetically stirred at room
temperature for 16 h. At the end of the reaction, the crude product
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10.1002/cctc.201902276
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Entry for the Table of Contents
FULL PAPER
M. Tejeda–Serrano, V. Lloret, B. G.
Márkus, F. Simon, F. Hauke, A. Hirsch,
A. Doménech–Carbó,* G. Abellán* and
A. Leyva–Pérez.*
CCl3
6
6
Br
Phosphorene
(0.005 mol%)
+
TOF0 > 7 s-1
CBrCl3
Page No. – Page No.
Phosphorene catalyses with extraordinary activity radical additions to alkenes,
faster than optimised metal catalysts, opening the door for future applications of 2D
heteroatom materials in organic synthesis.
Few–layer black phosphorous
catalyses radical additions to alkenes
faster than low–valence metals
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